It's pathetic because it's only in his head. And if you were to have a daddy figure (which isn't always a bad thing in itself), at the very least get the know them first.
He didn't get a chance to know him better. He only had those six months which, apparently, were just enough to get the idea of him that he had and some of it might be his imagination as it often happens in the absence of somebody you idolise. Seems whatever love he got from Duncan, it was still more than most gave him. Eamon let him sleep with dogs, for gods' sake, and instead of showing some backbone when it was needed sent him to the Chantry when he was a little boy, just because there were rumours. Isolde treated him like dirt. (And Alistair doesn't even hold it against her or Eamon.) That's a boy that had no parents to begin with because his own father abandoned him and he doesn't even know his mother didn't die but did the same thing. He was abandoned and unwanted. Repeatedly. So, yeah, maybe, just maybe his priorities are a little messed up in this department. Big surprise.
He needs to get to know a lot of things, in fact.
He does. Most of the characters in the games do. In fact, most people much older than him in real life do. During the talk with the guardian of the ashes, if you're too hard on yourself, it's Alistair who tells you nobody's perfect. I think he has a point.
I mean, all right, you don't like him. And you don't like him for these reasons. It is your right, of course. But honestly, I'm quite surprised you're so adamant about this and so hard on him, yet somehow tolerate Isabela despite lying to you and betraying a whole city, thus helping cause death of many innocents, just because she thinks of nobody but herself. But Alistair's emotional issues are too much to deal with, even though he's otherwise doing his best and doesn't really impact anything negatively? I'm sincerely not sure I understand. I don't think Alistair's flawless, but I've seen you judge who you consider a man-child harsher than I've seen you judge an actual criminal and person of poor character. I'm not sure I will even be able to understand.
I suppose our opinions on the matter are bound to differ.